I actually made the first version of this stove about 4 years ago while researching information on compact wood-burning downdraft gassifier stoves. The original version I made was too large and heavy for backpacking, but it gave me the basics for what would work for gassification (which, from what I understand, is when the burning wood is converted into gas, which in turn burns as the stove's primary fuel source. A wood downdraft gassifier burns, counterintuitively, downward, and the released gas is sucked through the bottom, pulled up through the double side walls, and released as a flame through the top vent holes. Ideally a wood downdraft gassifier should burn with blue flames, something that I have not yet achieved in my designs). When I saw Ryan Jordan's reiteration of what I thought had been the defunct BushBuddy stove, I decided to try my hand at a lighter version of my original stove. Below is the result.

The stove is made of two tea cans with airtight lids, one fitting with about a fingerswidth of space around the perimeter, inside the other.

I cut holes around the base of the big can and holes near the lower rim of the small can. Then I cut out the base of the small can, turned it over so that the can's opening was facing downward, and placed a circle of mesh at the bottom. I cut a hole in the big can's lid so that the small can fit just right, then fitted the small can and lid to the top of the big can.

The whole thing, including a titanium pot stand, weighs 180 grams (heavier than Ryan's Artic stove). It fits easily inside a 0.9 liter pot.

To stabilize the stove I can either hook two titanium stakes to the sides of the pot stand, or push four stakes through holes running through the stove into the ground.

The whole project took about an hour to make with simple tools: a pocket knife, file, metal cutter, hammer, pliers, and nail. I haven't ried it out for actual cooking yet... a little wary of coating my expensive titanium pots with the resulting soot, though that soot is supposed to make the pots more efficient...

Edited by butuki on 06/14/2006 20:16:25 MDT.

Nicely done, Miguel. FYI, if you're ti Pot is NOT the non-stick lined kind, I recently found an easy way to get the soot off... set the pot, empty, on a butane stove (snowpeak giga ti, etc) and let'er'rip... burns the soot right off and leaves the pot unharmed (other than a cool bluing effect)

Not this ONLY works with pots that are JUST ti, no rubber handles (which as I type this I can't remember if your's is) no non-stick lining. IMO, the best pots for this are the Snowpeaks...

Nice stove Miguel,

I may try out this stove idea with some other cans and see if it works, I like the whole wood stove idea, but so far out of the ones I have made, one is too large and heavy, and another is small, it works , but can be hard to light. and can only hold a little wood at a time, so you have to keep refueling.

Thanks Joshua for the inforamtion about getting soot off the Ti pot. Since my pots don't have a coating inside your suggestion just might work. But I think that I might just dedicate one of my pots to wood stove cooking. The soot will make the pot more effective.

Ryan, I, too, have wondered about using a small wood stove. I've successfully used the fan-driven zip stove for hiking and I suspect the stove I have shown here can do the same. The pencil-thin lengths of wood used to fuel the fire are small enough that collecting them around the area where you would use the stove presents little problem for obtaining enough fuel, and feeding the stove with such small kindling really doesn't take a lot of work. My only concerns are if it would be more difficult after several days of heavy rain and if I could maintain enough fuel while climbing in alpine regions, without disturbing the fragile habitat.

Downdraft gassifers, unlike simple, single-walled wood stoves, are lit from the top. Once the wood gets burning the red-hot layer of embers at the bottom of the stove serves to turn the burning wood into wood gas, which is the fuel that runs the stove. It's similar to the gas put out by liquid fuel stoves.

Miguel, You said "The stove is made of two tea cans with airtight lids"

Are these "Tea" cans Matcha tea? I have a bunch of these but they are a little heavy. Most of mine are the smaller size cans as the tea stays fresh if it isn't opened. I do have a few empty larger cans put away someplace and I have a few other cans that look like the type you used for the inside.

I might try a stove made from one of my tea cans. I would cut the bottom off the can and use it but replace the side of the can. I would make a new side out of Aluminum or Titanium. Then I would use the cap from the can and see if I can lighten the stove a bit.

Hi Bill. How are you holding up these days? Are your treatments getting any easier? I do hope that you will finally be able to get a full recovery soon and you'll be able to get out to the mountains for your walks. After all, you're making all that equipment for a reason!

The inner can is a Chinese jasmine tea can made of a steel that is slightly thicker than that used in soda drink cans (the macha tea cans I've bought tend to be made of heavier steel). The outer can is a generic tea can that I found at a thrift shop. The steel is heavier than it need be, but since I don't have access to a lot of titanium without spending an arm and a leg, I just went with this for now. I think your idea of using titanium would be great! Certainly would make the stove a more reasonable weight, but I also figure that since I wouldn't carry a fuel cannister or fuel, the weight of a wood stove is offset by the weight savings in not carrying a cannister/ fuel bottle, or fuel itself. The downdraft gassifier burns very hot, with the top vents actually shooting out flames, much like with an open top alchohol stove. Just one caution... make sure the grating at the bottom of the inner can is open enough to allow the resulting ash to fall through and to allow as much air to get into the inner can as possible. By having a removeable top it is easy to clean out the accumulated ash at the bottom.

Here is the original article I first referenced when starting to research inverted downdraft gassifier stoves.

This article was also very helpful for ideas.

Miguel,

just to confirm, you've made an inverted downdraft woodgas stove without the gas wick, correct?

Joshua, actually I'm not exactly sure what the "wick" is. I think it's meant to mean the air space between the double walls of the stove wherein the wood gas rises from the bottom of the inner can, up along the sides and out of the vents at the top of the inner can. The "wicking" I think refers to this movement of wood gas through this "flue". I don't think it's a physical wick. The Bushbuddy also has this double wall construction. It's the double wall that is important, and why the single wall wood gas stoves I've seen seem to be missing a key component. At least that's how I think this all works.

Edited by butuki on 06/14/2006 09:25:21 MDT.

HOw do you light the stove.

do you have to use a starter fluid?

I just made a double wall wood gas stove, based on Miguels stove above. I have not tested it and dont have a pot stand yet, But I think it is a good little design, it took about an hour to make, and weighs 5 oz. And fits in a snow peak 900 mug
The space between the two walls and the bottom of the inner and outer cans is only about 1/3", I dont know if this will make it so the stove performs poorly.
Here is a picture of the holes on the inner wall


I did not have any wire mesh so I drilled a bunch of 1/4" holes in the bottom of the inner can. It worked on other wood stove designs, so it will work fine...I think


I used a progresso soup can for the inner wall, and a pumkin can for the outer wall, (the 31oz bean can on the right is the exact same size as the pumkin can)


I am working on the pot stand and will test it, and post some pictures of the stove in action this weekend

Edited by ryanf on 06/14/2006 14:31:51 MDT.

Hey cool, Ryan! I think maybe your design is lighter than mine, so I might give the food can idea a try.

The stove is lit from the top using tinder that is pushed inside a little. No lighting fluid needed. Tinder can be anything like dry white birch bark (easily found hanging in strips from the trees), shaved wood (this is where a knife, even a small one, comes in handy), small, dry pine cones with lots of resin, dry pine needles, dry leaves, or, if you can find it, bits of the tinder fungus (those saddle-shaped funguses that grow on the sides of old trees). The pencil thin lengths of kindling that you use to keep the fire going are so small that lighting them is no problem. For further information on lighting wood fires without modern methods see Bushcraft UK. Ray Jardin's book, "Beyond Backpacking" also has some information on lighting cook fires.

While I don't know exactly how much space is needed between the outer and inner cans, I do have a few concerns. Since there is no way to easily remove the inner can from the outer, you might have some trouble with cleaning out the accumulated ash from the bottom of the can. In the BushBuddy design a separating bottom with the side vents punched in is used beneath the stove proper. Also, I've tried the hole-punched grating and the ashes tend to clog these up fairly quickly. If you can find mesh grating somewhere it would improve the airflow significantly. And last, I'm wondering if maybe the inner can sits a little too far down toward the bottom of the outer can. Is there enough air flow here? Remember ashes will fill this space.

I'm looking forward to seeing the stove in use. Please post pictures!

Edited by butuki on 06/14/2006 19:58:39 MDT.

Miguel and Ryan: Really neat stoves! I've read about these types of stoves before but never thought to make one. I may give it a try. I really can't wait to see what Bill Fornshell comes up with!

I've got a Kelly Kettle myself and like it except for the bulk. The weight is actually not too bad when you consider it replaces a stove, pot, fuel container, fuel, etc.

Dale Coryell of Wilderness Access posted on the user reviews that he uses fire starter sticks. I never though to use these before. I went down to Safeway and bought some Diamond brand fire starting sticks:



Each stick (you can actually light it as a match) is flattish and about 6 inches long. One stick weighs 0.8 oz and can be devided into 12 pieces to get a pretty good chunk for starting a fire. I did a couple of tests with these small squares and was quite impressed. Each small square will stay lit easily for 5 minutes. What really impressed me though was how easy they lit. When you break a chunk off it leaves a fuzzy edge. I was easily able to light the chunk by directing some sparks to the fuzzy edge with a light my fire starter. The package says this stuff is just compressed sawdust and wax so it has no noxious fumes too.

I actually like this stuff more than the tinder quick tabs sold on this site. They light just as easy but stay lit longer. I'm adding this stuff to my fire starting kit.

Miguel,

Do you think drilling some small holes on the inner cans side at the very bottom would help? The two can bottoms are about 1/3 inch from each other that may not be enough, some holes on the side bottom may help

hope I explained that OK?

Daniel,

when I test it I will use some starter sticks I have similar to those, you posted.

Edited by ryanf on 06/14/2006 20:08:22 MDT.

Hmmm, Ryan, I dunno. I've never tried it. It might work. I guess all you need to keep in mind is that you want as much air flow as possible there at the bottom. Why don't you give it a go and see what happens? Since it's only the inner can that needs working on, it shouldn't be too much trouble fashioning a new inner can to fit into the outer one if something should go wrong.

You might also want to try one of those steel sink drain grates.

Edited by butuki on 06/14/2006 20:11:06 MDT.

I lit up the stove this afternoon, but right after lighting it, I found my camera was out of charge, so no pictures, sory.

I tested it anyway.
I was very happy with the performance the gassifacation was a sucess.
Before teting I cut larger holes in the bottom of the can, actually I cut between holes with a pocket knife so instead of a bunch of small holes they are combined to make fewer, larger holes.(I will post a picture)THey were not clogged by ash.
anyway, I lit the stove using a colgahans fire stick and grabbed a bunch of dry wood, broke it in to small peices, threw them in the stove, light the stick and in a few minuets I had a nice fire going, I was afraid that there would not be enough room for the wood gas to come up the sides but it worked and the flame was not coming from the wood it was coming out of the holes in the top of the inner wall like Miguel described they should. I was very impressed, The flame burned hot, burned the full can down to coals, and lasted for mabey 10-12 minuets without refueling. And the flame at the hihgest was about a foot tall.

This is a great stove, I will make a potstand for it and use it for boy scout campouts, and hikes where low weight is not important because we are not moving fast, or at all.
And I dont want to spend $$$ on alc. or esbit for just an overnight campout.
again, a great stove other styles of wood stoves dont compare, sorry again for no pictures

Edited by ryanf on 06/17/2006 14:15:52 MDT.

Hey, Ryan, I'm confused -- is this stove running on wood or beans? --- I don't get the "gas" thing.

Seriously, nice job using recycled cans. For an overnighter, I wonder if some sort of charcoal stove would work. A few briquettes would put out some heat and be light and cheap.

Hi Dale, take a look at the link to the woodgas stove concept above. It explains in detail how it works. It's not just the wood itself burning, as in regular wood stoves (note those are not "woodgas stoves). It's much hotter, cleaner, and more efficient. It's why Ryan J. took the Bushbuddy to Alaska. The concept is not really intuitive at first. But when you use the stove, as Ryan F. did, you will see the gas burning as jets from the top holes in the stove.

I'm not sure if others understand that you don't need an extra windscreen for this stove, though a layer around the opening under the pot would help with conserving heat. The outer can acts like a windscreen. Because you don't need a windscreen, or carried fuel or fuel container, the stove is lighter than alcohol, gas, or cannister stoves with their extra containers and fuel requiements. Ryan J. expains about this on his Arctic 1000 site. If you learn bushcraft and how to obtain dry fuel even in the rain, this kind of stove could be an ultralight walker's dream. I'd just like to get the materials even lighter, and learn more about how to get the woodgas to burn blue... the epitome of the stove design's efficiency.

These kinds of stoves burn all kinds of fuel. I just don't know enough about the chemistry and physics behind it to be able to say if things like charcoal would produce wood gas. Anyone else have any idea?

Edited by butuki on 06/19/2006 23:55:48 MDT.

Check the stoves "Discussion List" at www.repp.org for _extensive_ discussions of TLUD (Top-Lit UpDraft) technology, including the elusive blue flame. Note especially the contributions of Tom Reed (also offering a battery powered woodgas campstove at www.woodgas.com), Paul Anderson and Alexis Belonio. ALW

I was kidding--- "gas," "beans".... geez guys.

It's a great idea. I like the fact that it doesn't use a fan or batteries-- less "gizmo" factor. What about using these stoves where there is a burn ban in effect? I could see a ranger having fits.

The charcoal idea was more of a tangent concept rather than using it directly in the wood gas stoves. Titanium hibachi anyone?

Ryan,

I was wondering if you tested the cooking speed of your stove?

ie ... How long did it take to boil a pint of water on it?

Also notable are the contributions of Ray Garlington: http://www.garlington.biz/Ray/WoodGasStove/

and Mark Jurey:
http://www.csun.edu/~mjurey/pennywood.html

I have made both of these stoves (in 5-15 minutes), and they do a remarkably efficient job of burning wood without smoke, without the double wall. I'm not sure the double wall is worth the effort for most occasions.

ALW

Wow-- those are so simple! Is it possible to make one of these where the pot can sit down in the stove a bit and use cross-wise stakes to support the pot?

Rig it up however you like. They're surely not as efficient or hot burning as your ingenious double-walled version. The most important aspect of them is the "top-down" burning. If it weren't for this, they are little more than modified hobo stoves, which work by limiting convective heat loss. Having spent many weeks trying to perfect their use under wet conditions, I can say that they do a little better than a simple cooking fire. But any wood stove is no substitute for basic wood craft.

The true champions of efficient wood burning for cooking are the fan-powered cook stoves by Belonio and Reed. Without a fan, there will never be blue-flame, carbon-monoxide free efficiency. See the recent posts by Anderson and Reed on the www.repp.org "Stoves" "discussion list." But these folks are working with impoverished rural populations where fuel shortage is a problem, and smoke is intolerable (as they will be used inside the home like our ranges). Such efficiencies are not needed in the backcountry where smoke is easily dissipated and fuel relatively abundant.

A more ambitious goal might be to develop a wood-burning stove that is acceptable to forestry officials for use in burn-ban areas. As it is, a properly contained wood fire is as safe as an alcohol, esbit, or gas stove (all will wreak havoc if fuel is spilled or kicked) and does burn only a handful of twigs to boil a few cups of water. Is anybody up to addressing this regulatory issue? ALW

Nicely done. I had (at one point) tried to make a similar integrated unit stove, but ran into problems as (I believe) mine had a much smaller annulus space than yours did.

Not having enough time to refine my idea, I'm glad to see someone else did.

I suspect that your design could be refined so that a group of boyscouts could make a similar design without the need of power tools (using a church-key can opener, a hold punch, a side-cut can opener maybe a couple other things... some tins snips...) I may need to find some similar-sized cans and try it out.

Miguel, I was just relooking at your pics. Am i wrong, or is the bottom of your 'firecan' (the inner can) solid? did you not put mesh in the bottom? does the ash simply collect in the bottom and you dump it out at the end of the burn?

Hi Joshua, you picked up that little unfinished business in that picture. :P When I took the first indoor photos I hadn't yet found a grating for inside the inner can. Since then I found a lightweight steel drain cover. It's being used in the lit stove picture.

This weekend I will be getting out to the mountains and trying the stove out. I'll bring a backup cartridge stove just in case. SInce it is the middle of the rainy season here, my woodcraft skills will be nicely tested... hope I can find the dry fuel I will need for the stove!

Ah, good... I was afraid I had missed something in my understanding of gassifying stoves.

No problems then...

Yes, I too am grateful for the explaination. :)

I just built and tested a stove based on Ryan's model. Very impressive--clearly burning the wood gas. Very hot, very efficient, no smoke. The flame was not blue, but was jetting from the holes in the inner can.

I wonder what the burn pattern would be if the holes in the inner were smaller.

On the bottom of the inner can, I just cut big holes will a razor knife for ventilation.

As always, thanks to all for the great ideas and techniques. The forums on this site are a treasure.

thanks for mentioning the absence of smoke when using the stove, I remember this now that someone said it, I guess I just did not notice while using it, Another great advantage to this design.

I completed the final peice of my stove last night, the pot stand.

I am not sure If it will hold up in high heat I would test it, but it has been raining for the past 4 days and is supossed to continue for the rest of the week

I made it from an aluminum film canister

here is a picture on top of the stove

It is removable

and rolls up to fit in the stove




I also made a change in the fire grate, I made larger holes in the bottom of the can


and am using a thin titanium stake to suport the inner can to make more room for air to flow


here are a few more pics.





the final dimensions are 4"X4.75"

Edited by ryanf on 06/27/2006 09:56:20 MDT.

If anybody has the time and cash to burn...

Try making a similar stove out of a double walled titanium mug. Try starting with Snow Peak's 21fl.oz (4.4oz) or 15.8fl.oz (3.5 oz) double walled tall stackable cups (http://www.snowpeak.com/gears/tw-stackablecupspage.htm).
---smaller seems impracticable. These are starting weights. Some material will be taken away, and a little added-so they should be close to a finished weight. The price (sans labor) is still less than a Bushbuddy.

1. Remove the handle assembly (if not starting with stackable cup)
2. Cut the majority out of the outer bottom--but leave the lip for strength.
3. Cut the inner bottom out about 1/2-3/4" from the bottom and replace with lightweight SS hardware mesh, or weave your own out of SS wire (or simply pepper the intact bottom with 3/16" holes, ala R. Faulkner's stove).
4. On the outside, Drill 3/8" holes 1/4" from the bottom all the way around w/ 3/8" gap (experiment for best dimensions)
5. On the inside, drill 1/4" holes all the way around with 1/8" gaps (or whatever makes it an even fit--make a template) about 3/4" from the top.
6. For a pot stand, try fashioning some apparatus with titanium wire that will sit over the lip.

From what I've read by those who have designed such stoves, that the size of the holes and their placement matters a lot for the performance of a particular sized stove. I don't know the formulas, but you could search www.repp.org's stove discussion list for assistance, or write to Tom Reed or Paul Anderson.

One could practice with tin cans to get the best setup, then transfer the dimensions to the expensive titanium. There are also many cheaper stainless steel double walled cups that could serve to practice on.

Just an idea--any takers?

Edited by alarswilson on 06/27/2006 18:18:16 MDT.

Andrew,

I've considered a similar design myself out of the doublewall stackable cups as they don't have any handles to remove. However I believe that working the holes into the inner wall will be trickey.

I have also considered using the Ti Single Cup (II) (one of each) as I believe it would be easier to work the inner and outer cans seperately and these two should (I haven't actually seen them in real life) stack with plenty of annular space for air movement.

Edited by jdmitch on 06/28/2006 08:42:54 MDT.

has anyone considered or tried making a wood gassifier with a beer can outer and a small steel can inner to save on weight. I am thinking of using a heineken can for the outer. It might be hard to find a lightweight steel can in the right dimensions for the inner though. How hot does can the outer get on the stoves made so far? Would it be hot enough to warp/melt aluminium?

The outer can would certainly not get hot enough to melt/burn aluminum--it may char if touching the inner can at the top. Ask Ryan F. how his aluminum pot stand worked--that should let us know if it is a servicable material. ALW

Cheers for the reply Andrew. Ill have to give it a go as soon as I get through this beer.

I am also thinking of using mesh for the top half of the inner to save on weight, which will extend past the top to act as a pot support. But I will see how hot the outer gets first-that might be pushing it too far. Especially as the most available fuel for me is Eucalyptus (In Australia) which burns very hot.

The minimal research I've done into wood stoves showed that they threw small amounts of spark into the air immediately surrounding the stove. However, seeing as how the models we are particularly discussing are gassifier stoves my information may not be correct.

I tried tin can versions, but found them not easy to light. Then, along came the littlbug (note there is no "e"). I found it easier to light the fire on the ground without the can or chimney. As soon as it gets going put the stove on top. Design your sove without a bottom. If you do not want to do that and have your stove portable while lit, or not scarring the ground, I would suggest designing the stove so the the match can be held underneath the tinder. The flame has a larger area of tinder to ignite. If building a fire on the ground, just dig out a small trench with two fingers, making it easy to get the match underneath. Use the lid of your pot to fan the flames.
http://outdoors.webshots.com/album/556839194qbaYfz
Have you seen the chimneys used to light charcoal for grill cooking. There is a space for tinder (newspaper) to be lit underneath the charcoal. The charcoal sits on a small grate a few inches above the bottom where there are also vent holes. BTW for tinder look for the lowest dead branches on evergreens, like hemlocks. A handful of the smallest twigs on these branches, still attached to the tree, ignite easily.

Edited by rambler on 02/24/2007 16:27:12 MST.

The real Bush Buddy is a highly refined stainless steal stove that weighs 6.5 oz., and burns wood cleanly and efficiently. By analyzing its structure, we can re-create its effectiveness from cans. I've written an article on how to do it for the next issue of Wilderness Way Magazine: http://www.wwmag.net/features.htm . Meanwhile, here are a couple images of it:
Parts: Outer Can: 4" dia x 4.75"; Inner Can: 3.5" dia.x cut height with large bottom hole with four each tabs bent: up and down; Ash Tray: 3" dia x cut height with 4 side-pressure tabs; Half-inch hardware cloth grate inserted into slits for corners; Pot-holder/windscreen: 4" dia x 2" tall, turns over and slides between inner and outer walls for travel, and all fits into billy-can (4.25" dia x cut height to fit) opened with seal-cutter so lid can be re-used. Air-flow spaces all at least a quarter inch. Ashes build up an inch before blocking flow; revive by shaking. Bottom doesn't get too hot for raw-wood surface like picnic table. Easily moved while burning with pliers of multi-tool. Releases almost no sparks even in moderate breeze.

Yes I have done it using a 2 litre aluminium japanese beer can as pot and outer jacket The printing discoloured but the aluminium never got close to melting. see this thread. http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=8025&disable_pagination=1
My pot windshield and stove all nest and weigh a total of 200 gram

I've simplified and lightened my design with a single 4" x 6" can.
A grate doesn't have to be continuous. These lower draft hole flaps, bent in, hold up most of the wood, allowing coals and ashes to drop into solid-bottom ash tray, so heated air comes up under wood for a clean burn. Same size vents above let flames lick pot on their way out. Ample door (2 1/4" wide by 1 3/4" tall) allows feeding of large wood plus more air exchange.
Single piece is strong, light, leaves no trace, no parts to lose or abuse. Burns fast and clean. And of course it needs a small aluminum wind-screen if used in an unprotected place, to prevent embers from getting blown away by a freak wind.

Edited by Can-CanBushBuddy on 08/04/2008 20:55:20 MDT.

I;m glad they did away with the terminology of Down Draft to describe the stove. Notice that most of the authors sold their own version of the stove. The double wall thing is hype. The wick glows red hot and acts as a catalytic burner of a type to consume all gasses going up and out just as in the common kerosene space heaters.
.

Edited by zelph on 08/05/2008 16:29:38 MDT.

Okay, now I'm just confused.

So the whole Double-wall Downdraft concept is just an illusion? Are they not any better than Hobo Stoves?

I was about to start making one until I read Dan's post on this and the other thread: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=8025&disable_pagination=1

Is best stove to have the main fire raised above the coals collecting at the bottom and anything other than that is just superfluous (such as a double wall)?

Here is a piece of information in regards to the woodgass stoves:

I was happy to see an updated description/terminology being used in the quoted preface (quote)

RICE HUSK

GAS STOVE

HANDBOOK

Alexis T. Belonio

With “Preface” by Paul S. Anderson



PREFACE

The importance of this “Handbook” and the work of Engr. Alexis

Belonio should not be underestimated. I have been given the honor to write

this Preface, and my intent is to illustrate the importance of this work.

The search for technology for clean combustion of low-value dry

biomass in small stoves suitable for residential cooking has been ongoing

for hundreds, if not thousands, of years. One relatively new technology

was identified and initiated in 1985 by Dr. Thomas B. Reed. He originally

called it “Inverted DownDraft” (IDD) gasification, but recently we have also

called it “Top-Lit UpDraft” (T-LUD) gasification, a name that more clearly

denotes what is actually happening in this combustion technology. The terms

“gasifier” and “gasification” refer to having any type of combustible gases

from dry biomass created distinctly separate from the combustion of

those gases, even if the separation is only a few millimeters and/or milliseconds.

Developments and adaptations of Dr. Reed’s IDD or T-LUD

technology during the past twenty years have been slow, mainly without

commercial products, but discussed and shown occasionally as a

combustion curiosity on every inhabited continent.(end quote)

I believe the double wall to be insignificant when it comes to our little backpacking size stoves. I removed the double wall from my Zip Stove and tests showed it heated 2 cups of water faster than with a double wall. 3 seperate tests per stove were done on the same day, same conditions. A unmodified Zip against my modified one. Same amount of fuel by weight(clothes pins/kiln dried=)) The single wall Zip was more efficient. Both zips had their fan setting secured on the half throttle setting while stoves were under test.

Edited to add link to thread Modified Sierra Zip Stove

Edited by zelph on 08/08/2008 16:42:59 MDT.

Zelph,
I'm with you on the wood gas issue: Single wall is just as efficient as double wall, all other factors being equal, including outside size. In my somewhat primitive tests the single-wall was also lighter, held more fuel, lighted and powered up quicker, created less soot and could store more stuff inside.

As far as I could tell, the largest performance gain in stoves using the same can size came from elevating the fuel to improve oxygenation. In the single wall, this was achieved with a hardware cloth grate.

I just made my own hobo wood stove out of a small coffee can. Half way through my first test with it I remembered that some metals give off toxic gas when put next to or into fire. Would I have to worry about toxic fumes from my hobo stove?

Vick,

What you and Dan don't seem to understand is that a fire in a can has no sex appeal. Add an extra wall and give it a cool (if wholly inaccurate) name and you have something you can talk about all day in forums and get a lot of wows on the trail :) Maybe if they put a small dish antenna on the side of single walled stoves they'd have more appeal.

H

Edited by herman666 on 02/27/2009 07:23:26 MST.

Herman, I think you are absolutely right. =)

Everyone should go back to making the double walled downdraft gassifiers. Add a few bells and whistles. Remote piezo ignition systems, .001 Titanium throughout, auto ash dump when stove is folded for storage. =)

Now you're back to square one and alot more sex appeal. It's what our society is all about, it's what sells product. Put more holes in it to make it look "tactical" Vary the shape of the holes to make it have more "sex Appeal"

> Vary the shape of the holes to make it have more "sex Appeal"
Heart shapes?

Cheers

Yes, heart shapes for the female DIY's in the forum if any. Hole quantities can be 38 on top. 22 in center and 30 on bottom. Shape the stove in an hour glass form. I'm sure the "Stuff Sack" could be made in an interesting fashion.

I'm sure the "old School" can make it happen. ;)

some real nice creations, first one in this thread looks real professional. ive simply called them chimney stoves after being basically a little chimney or similar to the chimney charcoal starter. in essence you have a small wood burning fire where heat is directed straight up and air flow is provided through holes in containers wall.

i considered building one of my own but opted for a built model that disassembled and can be nested inside of a pot. its the littlbug and works very well. i dont think ive seen a diy hiker make one quite like that yet but it makes a lot of sense due to packing space.

due to limitations at certain hiking trails/shelters im now having to build an alcohol stove so smoky the bear wont eat me.

There seems to be some huge dumping on the whole idea of wood gassification on this thread which I find unusual.

Regarding the zip stove tests with single wall. That is not a wood-gas stove, it is a forced air stove. Whether or not gassification does or does not occur is really irrelevant given the tremendous heat the forced air generates.

Second, wood gassification is science, not fashion. There has been millions invested in wood gas stoves the world over. If there is some question as to the validity of some designs I suggest discussing those issues specifically, not dismissing wood gas all together.

Third, stoves can burn fairly cleanly with a single wall if they run hot enough... as with a fan. But this is not always the case (i.e. in the middle of winter, with wet wood, or in the wind.)

Fourth, the job of the second wall has many purposes

- protect the fire from elements like wind and rain

- insulate the fire and reflecting heat back into it to make it burn hotter

- preheat air and deliver it to the secondary combustion zone at the top of the burn chamber thus burning any remaining gases and therein reduce smoke. (Think of it like a pilot light system on a smoke stack.)

What's more a good system like the Caldera Tri Tri Inferno also does one more thing. It actually acts like a windscreen for the pot to ensure it heats from sides as well as the bottom.

Regarding the very last post. By a "chimney stove" I can only assume you're talking about a *rocket stove*. Wood gas and rocket stoves are two completely different types of stoves that function on different principals.

Specifically the rocket stoves only intake is at the bottom and it burns ONLY from the bottom. It burns well because it produces a tremendous amount of convection that sucks in fresh oxygen.

I realize when these concepts are applied to tiny ultralight stoves they can end up all looking the same. Even more confusing their are definitely some claiming to be wood gas that actually may not be so effective in this manner so it helps to understand the intent of the stoves creator before critiquing them.

What I find so interesting and potentially confusing is that you can produce some pretty decent gassification in good conditions with a single wall stove. These break a lot of the "rules", but they're still based on the basic principals of wood gas.

To make matters more confusing there are many types of wood gas. Most of those posted here are generally called inverted down-draft wood gassification stoves though some have suggested there might be other more appropriate names rather then "inverted down draft" which sounds like an oxymoron.

What inverted down draft simply means is that the standard means of gassification have been inverted and the draft in the burn chamber flows down... theoretically. Depending on the quality of the stove, and conditions such as the quality of the wood and you can at times see the smoke seem to hover in the burn chamber below the flames at the top of the stove. It's then that the stove is working perfectly.

Wikipedia has good articles on both wood gas and rocket stoves that should help clarify the matter.

Edited by mmeiser on 11/26/2009 22:24:12 MST.